The present invention is generally and widely applicable to the formation of electronic device materials, for example, for semiconductors or semiconductor devices and liquid crystal devices. Herein, for the convenience of explanation, the background art relating to semiconductor devices will be explained as an example.
Substrates for semiconductor or electronic device materials including silicon are subjected to various types of treatment such as formation of insulating films including oxide films, formation of films by CVD or the like, and etching.
It is not too much to say that an improvement in the performance of semiconductor devices in recent years has been achieved by virtue of techniques for microfabrication of the devices including transistors. Even today, an effort is still being made to further improve the transistor microfabrication techniques for higher performance. A demand for a higher level of microfabrication and higher performance of semiconductor devices in recent years has led to ever-increasing needs for insulating films with higher performance, for example, in terms of leakage current. The reason for this is that, in recent microfabricated, highly integrated and/or higher-performance devices, even a low level of leakage current may possibly cause severe problems, although such a leakage current does not pose substantially no problem in the case of conventional relatively low-integrated devices. In particular, low-power consumption devices are indispensable to the development of portable electronic devices in the so-called ubiquitous society (information-oriented society using as a medium electronic devices which can be connected to networks anywhere at any time) which has begun in recent years, and, to this end, a reduction in leakage current is very important.
Typically, for example, in the development of a next-generation or advanced MOS transistor, with the advancement of the above microfabrication technique, the possible thickness reduction of gate insulating films has approached to its limit, and, consequently, a severe problem to be overcome has appeared. More specifically, according to process technology, the thickness of a silicon oxide (SiO2) film, which is currently used as a gate insulating film, can be reduced to the maximum (level of 1 to 2 atomic layers). However, when the film thickness is reduced to 2 nm or less, the leakage current due to a direct tunnel by quantum effect is increased exponentially, so as to increased the power consumption disadvantageously.
At the present time, IT (information technology) markets are being transformed from stationary electronic devices typified, for example, by desktop personal computers and home telephones (devices in which electric power is supplied from a receptacle) to “ubiquitous network society” in which electronic devices are accessible to the Internet and the like anywhere at any time. Therefore, in the very near future, portable terminals such as portable telephones (cellular phones) and car navigation systems are considered to be mainly used. Such portable terminals per se are required to be a high performance device. At the same time, requirements for small size, lightweight, and functions capable of withstanding use for a long period of time should be satisfied, although such requirements are not very important to the above stationary devices. Therefore, in portable terminals, reducing power consumption while improving performance is very important.
Typically, for example, in the development of next-generation MOS transistors, enhancing the level of microfabrication of high-performance silicon LSI poses problems of increased leakage current and increased power consumption. In order to reduce the power consumption while enhancing the performance, the characteristics of MOS transistors should be improved without increasing gate leakage current in the transistors.
The formation of a good-quality and thin (for example, a film thickness of not more than about 15 A (angstroms)) insulating film is indispensable for simultaneously achieving an enhancement in the level of microfabrication and an improvement in characteristics.
However, the formation of a good-quality and thin insulating film is very difficult. For example, an insulating film formed by conventional thermal oxidation or CVD (chemical vapor deposition method) is unsatisfactory in any one of characteristics, i.e., either film quality or film thickness.